Bring the cider to boil in a large pot over high heat. Cook until reduced to 2 1/2 cups or by half.

Add the pear chunks to reduced cider and cook until fruit is soft and translucent, about 30 minutes. Transfer to a food processor. Puree mixture until smooth.

In a pot over medium heat, combine fruit puree, the brown sugar and spices; stir to dissolve. Bring mixture to a simmer, adjusting heat and stirring frequently to avoid scorching. Cook until very thick, 30 minutes or more.

Remove from heat and cool to room temperature. Taste for seasoning and add the vanilla, if using.

Put pear butter into clean, hot canning jars, leaving 1/8 inch head space, and process in a boiling-water canner for 10 minutes, adjusting time for altitude.